A machine of this type can comprise, for controlling the percussion, a striker piston mounted to slide inside a cylinder which defines, around the piston, a first annular chamber connected by a "high pressure" pipe, to a one-way valve constructed in the form of a sleeve subject to the force of a spring and mounted to slide inside a chamber which is connected to an accumulator comprising a diaphragm and leading to which is a hydraulic fluid inlet pipe and a second annular chamber connected to a control valve with a slide having differential sections connecting said second chamber alternately to the "high pressure" pipe and a return pipe, control of the valve being ensured by a pipe connected to the cylinder.
This type of machine is described in particular in the published French Pat. Nos. 2 274 404 and 2 274 405 corresponding respectively to U.S. Pat. Nos. 3,908,767 and 4,006,665, over which the present invention can be considered as an improvement. In these machines the second annular chamber which is connected alternately to the fluid inlet pipe and the return pipe, by the control valve itself governed by the movements of the piston, has a useful cross section greater than that of the first annular chamber. The latter is permanently connected to the fluid inlet pipe when connection to the latter is established by the one-way valve. This valve, which is also in the form of a slide having differential sections, with a compensating spring, operates such that on the fluid inlet side remains less than a certain threshold value, the spring is slack and the valve closes-off the outlet of the "high pressure" pipe as well as the outlet to the accumulator.
When the pressure exceeds the threshold value in question, the slide moves, thus compressing the spring and releasing the outlet orifices of the "high pressure" pipe and to the accumulator.
This hydraulic device is satisfactory for controlling percussion, but it is not particularly well-suited for a rotary percussion machine, in which the drilling tool is not only struck, but also rotated. Naturally, it is always possible to rotate the tool by a mechanism which is completely independent of the percussion mechanism, which also has the advantage of allowing great operating flexibility, but necessitates two separate pumps and supply circuits. It has already been considered to mount the percussion mechanism and the rotary mechanism "in series" hydraulically (c.f. for example French Pat. Nos. 1 454 735 and 2 129 276 see U.S. Pat. No. 3,822,752), which makes it possible to have a single pump and also to simplify the hydraulic circuits. This solution is less expensive and more reliable, but it makes the rotation completely dependent on the percussion and in particular does not make it possible to rotate the drilling tool while withdrawing the latter, thus without operating the percussion.